Synthesis and characterization of SAPO-41: effect of the silicon content and the crystal size on the hydroisomerization of n-octane over Pt–Pd/SAPO-41

• Published in: Microporous and mesoporous materials Vol. 26; no. 1; pp. 161 - 173
• Main Authors: Mériaudeau, P., Tuan, Vu A., Lefebvre, F., Nghiem, Vu T., Naccache, C.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 16-12-1998; Elsevier
• Subjects: Characterization; Chemistry; Exact sciences and technology; General and physical chemistry; Ion-exchange; n-Octane hydroisomerization; SAPO-41; Surface physical chemistry; Synthesis; Zeolites: preparations and properties; Characterization; SAPO-41; n-Octane hydroisomerization; Synthesis; Mixed catalyst; Octane; Scanning electron microscopy; Hydrocarbon; Isomerization; Palladium; Zeolite; Experimental study; X ray diffraction; Supported catalyst; Molecular sieve; Platinum; Silicon Aluminium Phosphates
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/S1387-1811(98)00230-3

Silicoaluminophosphate SAPO-41 was synthesized either in the presence of surfactant or without added surfactant. Under the synthesis conditions with added surfactant small-size molecular sieve crystals were formed, while larger crystals were obtained in the absence of surfactant. Magic-angle spinning nuclear magnetic resonance spectroscopic studies showed that silica-rich domains existed for silicon-rich samples. Infrared spectra in the OH stretching vibrations and temperature-programmed desorption of ammonia revealed the presence of Brønsted acid sites. Samples prepared in the presence of surfactant exhibited higher acid strength. The hydroconversion of n-octane was perfomed over Pt–Pd-containing SAPO-41 samples. These catalysts showed high selectivity for the hydroisomerization reaction. Among the C
8 isomers, monomethylheptanes were preferentially formed. The selectivity towards hydroisomerization at constant conversion level did not change with the SAPO-41 crystal size. However, a small-crystal SAPO-41 sample was considerably more active than large-crystal SAPO-41. The shape selectivity of the tubular medium-pore SAPO-41 played the major role. Pore mouth catalysis at the interior of the pore is also discussed.